#include<stdio.h>
#include<iostream>
using namespace std;
int main(){
    const int x = 1;
    int b = 10;
    int c = 20;

    // const 修饰 int* 所指向的内容，但可以直接更改 b，不能更改 *a1
    const int* a1 = &b;
    b = 30;
    // *a1 = 40;
    // a1 = &c;
    cout << *a1 << endl;


    int* const a2 = &c;
    *a2 = 40;
    cout << c << endl;
    // a2 = &b;
    return 0;
}